Britain is to take in some of the most vulnerable refugees from the Syrian civil war, including torture survivors and victims of sexual assaults, Deputy Prime Minister Nick Clegg has announced.

No figure is being put on the number of displaced people the UK will take, but hundreds are expected to arrive over the coming year.

The UK is not signing up to take a quota of refugees under the United Nations sanctuary scheme to resettle up to 30,000 vulnerable Syrians in Western nations, but Mr Clegg said the UN High Commission for Refugees backs the Government's plans.

Home Secretary Theresa May will formally confirm the plans in a statement to the House of Commons tomorrow, ahead of a debate called by Labour, which wants Britain to join the UNHCR scheme.

Prime Minister David Cameron has resisted signing Britain up to the UN sanctuary programme, arguing that it is not the solution to a crisis which has seen millions of Syrians flee their homes in a three-year civil war.

He stressed that the UK was already the world's second-largest bilateral donor in the crisis, providing £600 million to help victims of the violence in Syria and neighbouring countries.

After coming under pressure from Labour and Liberal Democrats, he told MPs at Prime Minister's Questions last week that he was ready to consider taking in refugees in cases of extreme hardship. Ms May and Foreign Secretary William Hague have been working on details of the scheme over the past week.

Now Mr Clegg has said: "I am pleased to be able to announce today that the UK will be providing refuge to some of the most vulnerable Syrian refugees. The coalition Government wants to play our part in helping to alleviate the immense suffering in Syria.

"The £600 million we have provided makes us the second largest bilateral donor of humanitarian aid in the world. But as the conflict continues to force millions of Syrians from their homes, we need to make sure we are doing everything we can.

"We are one of the most open-hearted countries in the world and I believe we have a moral responsibility to help."

Explaining the criteria under which refugees will be selected for admission to the UK, Mr Clegg said: "The UN High Commission for Refugees - which backs our new resettlement programme - has said the highest priority should go to women and girls who have experienced or are at risk of sexual violence, the elderly, survivors of torture, and individuals with disabilities, so that's who we'll target.

"Sadly we cannot provide safety for everyone who needs it, but we can reach out to some of those who need it most.

"On top of that, we'll continue to support the peace talks currently taking place in Geneva, because only a political resolution between the (Bashar) Assad regime and Syrian opposition will provide a permanent end to the suffering.

"Britain has a long and proud tradition of providing refuge at times of crisis. This coalition Government will ensure it lives on."

No target will be set for the numbers of refugees to be admitted, with the UK instead working with the UNHCR on a case-by-case basis to identify those most in need of assistance.

Refuge will be offered to some of those most traumatised by the crisis, including vulnerable women and children, who are expected to arrive on a gradual basis over the coming months.

Shadow home secretary Yvette Cooper said: "Vulnerable Syrian refugees, torture victims, abandoned children and those struggling to cope or survive in the camps desperately need sanctuary and Britain has a moral obligation to help.

"I am very glad the Government has finally bowed to pressure before tomorrow's opposition vote.

"Compassion and common sense have prevailed over Government and ministerial resistance - and it is a tribute to the work of charities, campaigners and cross party support in Parliament that the Prime Minister and Home Secretary have reversed their position completely in the space of a week.

"The Government still needs to explain how the programme will work and whether they are signing up to the UNHCR programme or trying to run a parallel programme of their own.

"Given the considerable flexibility in the UN programme for countries to set their own priorities, numbers and security checks, the benefits of not running parallel bureaucracy and the value of being able to encourage other countries to follow suit, the Government would be best to sign up with the UN.

"In addition, ministers need to confirm that these will be additional places and will not be at the expense of help for other refugees.

"Finally it would be helpful for the Home Secretary to explain why ministers resisted for so long and to look urgently at removing refugees from the government's net migration target.

"Immigration policy is very different from Britain's long tradition of providing sanctuary for those fleeing persecution and the two things should not be confused."

The UK representative of the UN High Commissioner for Refugees, Roland Schilling, said: "We welcome the announcement of the UK government to provide refuge to some of the most vulnerable Syrian refugees, in cooperation with UNHCR.

"This decision will help to provide much needed solutions for vulnerable Syrian refugees many of whom have been deeply traumatised and face immense hardship.

"It is also a concrete and important gesture of solidarity and burden sharing with the countries neighbouring Syria as they continue to bear the brunt of the refugee crisis.

"Today's decision is an encouraging and important step, reaffirming the UK's commitment and contribution to international relief efforts in support of more than 2.3 million Syrian refugees and the countries hosting them.

"What's more, it also sends an important message to the rest of the world: Britain has a proud tradition of protecting and welcoming refugees and we will continue to lead the way in offering refuge to people in their greatest hour of need.

"We commend the Government for upholding this reputation by going the extra mile and offering protection to some of the most vulnerable refugees who will now have chance to rebuild their lives in safety.

"We hope other countries now follow the UK's lead by providing resettlement places to those who so desperately need it."

Amnesty International UK director Kate Allen said: "This move is long overdue but of course it's never too late to do the right thing.

"The government's line on this has been shameful, with months of refusal and weak arguments.

"It was a never a matter of choosing between helping refugees in the region or helping refugees in this country - and it's an enormous relief that the government has finally changed its mind on this.

"For some of the most vulnerable refugees, this offer is a lifeline. It's literally a matter of life and death.

"Today's shift from the government is testament to people power, with constituents contacting their MPs in their thousands about this issue."